A wireless communication device in a wireless communication system is provided with a power amplifier (hereinafter sometimes referred to as a “PA”) that amplifies power of a transmission signal. In a wireless communication device, in order to increase the power efficiency of a PA, the PA is generally operated near the saturation region of the PA. However, if a PA is operated near the saturation region, nonlinear distortion increases. Thus, in order to suppress the nonlinear distortion and reduce an adjacent channel leakage power (ACP), a wireless device is provided with a distortion compensation device that compensates the nonlinear distortion.
As a distortion compensation method that is used for a distortion compensation device, there is a “predistortion method”. Hereinafter “predistortion” is sometimes referred to as “PD”. In a distortion compensation device of the PD method, a signal having the inverse characteristic to the nonlinear distortion of a PA is added to a transmission signal before the transmission signal is input to the PA so that the linearity of the output of the PA is increased in order to suppress the distortion of the output of the PA. The signal having the inverse characteristic to the nonlinear distortion of a PA is sometimes referred to as a “predistortion signal (PD signal)”. Accordingly, the PD signal becomes a signal distorted in accordance with the inverse characteristic of the nonlinear distortion of the PA in advance.
For example, as a distortion compensation device of the PD method, there is a distortion compensation device that approximates the inverse characteristic of the nonlinear distortion of the PA by a power series and performs distortion compensation using the power series. Hereinafter distortion compensation using a power series is sometimes referred to as “series type distortion compensation”. In a distortion compensation device using the series type distortion compensation, an odd-order harmonic signal is generated from a pilot signal having a narrower band than that of a transmission signal as a PD signal, the phase and the amplitude of the PD signal is corrected, and the corrected PD signal is added to the transmission baseband signal before the transmission baseband signal is input into the PA.
A related-art technique is disclosed in Japanese Laid-open Patent Publication No. 2004-289504.